Franklin D. Roosevelt was the U.S. president from 1933 to 1945 who led the country during World War II. Winston Churchill was the British prime minister from 1940 to 1945 and helped lead the Allied forces against Nazi Germany. On June 6, 1944, the Allied forces launched the D-Day invasion of Normandy, France, a massive amphibious military operation that marked a major turning point in World War II.